As is known, for storage-stable epoxide resin mixtures there are used urons, such as monuron, diuron, fenuron and the like, for example in combination with dicyandiamide (cf. U.S. Pat. Nos. 3,562,215 and 3,956,237). A disadvantage in the case of the urons is the laborious production of these products, as well as the fact that, as accelerators, they are not able to lower the hardening temperatures of the epoxide resin masses as much as is desired.
Furthermore, imidazolides (N-acylimidazoles) (cf. Federal Republic of Germany Patent No. 32 46 072), as well as imidazoles blocked with isocyanate, have been described as latent, highly-reactive hardeners. Both types of compounds must be produced very laboriously by reaction with special acid chlorides, with the liberation of hydrogen chloride, or with isocyanates.
Imidazoles can be produced substantially more cost-favorably, for example according to British Patent No. 1,050,679, but they only possess a limited effectiveness or storage stability. Finally, U.S. Pat. No. 3,356,645 discloses special imidazole salts as hardeners which are formed from imidazoles and monocarboxylic acids containing up to 8 carbon atoms, for example acetic acid, lactic acid and the like. These salts are liquid and, in the case of comparatively long storage, change their color (dark coloration, oxidative decomposition).